52 PROTOPLASMIC ACTION AND NERVOUS ACTION 



oxidation-furthering enzymes (oxidases) extractable from 

 the cell have a relatively slight influence on the physi- 

 ologically important oxidations; e.g., of sugar. We may 

 thus regard the possession of a certain type of structure, 

 characteristic of the living state, as chiefly responsible 

 for the facility with which chemical reactions proceed in 

 living protoplasm, as well as for their modifiability 

 under stimulating conditions. The synthetic reactions 

 appear to be largely dependent upon the oxidations; 

 this is indicated by the importance of oxygen for growth 

 processes, as well as by various other facts, although the 

 precise nature of this interdependence is not understood 

 at present. The whole problem of the relations between 

 the structure of protoplasm and its chemical activity 

 is one of fundamental interest, and some of the more 

 general facts and considerations bearing on this problem 

 will now be briefly reviewed. 



CHEMICAL REACTIVITY OF LIVING MATTER AS 

 RELATED TO STRUCTURE 



All Hving matter is characterized by the possession 

 of a certain structural organization or permanent 

 arrangement of components which is essential to its 

 normal activity. ' If we destroy protoplasmic structure 

 by heat, mechanical injury, or chemical treatment, the 

 specific metabolic activity of the system and its respon- 

 siveness to stimulation are lost. 



In general, the chemical reactions of living matter 

 may be grouped under two classes according to their 

 relation to protoplasmic structure: (A) those reactions 

 which continue in an essentially unaltered manner after 

 the ^4ife" of the cell has been destroyed; e.g., in cell- 



